This invention relates to drainage devices and more particularly to underwater drainage devices of the type disclosed in U.S. Pat. Nos. 3,363,626 and 3,363,627. More specifically, the invention relates to the prevention of noise in such underwater drainage devices as disclosed in the aforementioned patents when used with suction wherein prior art devices substantial noise is produced by the device during operation by reason of air bubbling through the water in the manometer chamber. The present invention provides muffling means for reducing the noise produced by such bubbling to an acceptable level.
In our prior U.S. Pat. No. 3,782,497, there is disclosed a sound muffling device including a member which is inserted in the opening to atmosphere from the manometer chamber. This member is provided with a tortuous passageway extending therethrough and such device to a certain extent muffles the sound emanating from the device by reason of the bubbling of gas through the water in the manometer chamber. However, the sound muffling device disclosed in U.S. Pat. No. 3,782,497 is not entirely satisfactory in reducing the sound from underwater drainage devices to a level which is acceptable to patients. Accordingly, it became necessary to improve upon such device.